This invention relates generally to floating roof storage tanks, wherein the roof for the tank floats on the product stored therein. These floating roofs are provided with seal means at their peripheries to effect a seal between the roof and adjacent tank wall as the roof rises and falls with the level of product stored in the tank. While a floating roof is desirable from many standpoints, it does possess disadvantages. For example, water from rain or snow and the like can collect on top of the floating roof and if the water accumulates to a certain level, it may cause the roof to sink or cause structural damage to the roof. Usually, such floating roofs provide a drain connection with a normally closed valve, whereby the valve may be manually opened to drain excess water from the surface of the roof and thereby prevent sinking or damage to the roof. Under most circumstances, such an arrangement is generally satisfactory, since the accumulation of water on the roof may be observed, and when it reaches a dangerous level, an operator simply opens the valve to permit draining of excess water from the surface of the roof. However, an occasion may arise wherein the level accumulates very rapidly due to a severe storm or the like, and an operator may not have an opportunity to open the valve to drain the water from the surface of the roof, with the result that the roof will sink or be structurally damaged. On the other hand, even in the absence of a severe storm or the like, an operator may simply forget to open the valve to drain the water from the roof, and thus serious damage can result. A typical roof drain of the type which requires manual operation is disclosed in U.S. Pat. No. 2,563,017 to A. S. Field.
Another type of roof drain is disclosed in U.S. Pat. No. 3,606,071 to R. B. Wagoner, et al. and in this patent the roof drain comprises a siphon member which becomes operative only when the roof has sunk in the fluid and is resting on the bottom of the tank. Then, as the product stored in the tank is withdrawn, the siphon become effective to siphon liquid off the top of the floating roof.
The present invention is designed for use with a conventional drain valve, such as shown in U.S. Pat. No. 2,563,017, for example, wherein normal collections of water on the surface of the roof may be removed by opening a manually operated drain valve. However, if an operator should forget to open the manual drain valve, or if a severe storm results in a rapid accumulation of an excess amount of water on the surface of the roof, then the emergency drain valve of the present invention becomes operative to drain the water from the roof.
More particularly, the drain valve of the present invention operates on the siphon principle and ramains closed and does not effect draining of water from the roof until the level of the water reaches a predetermined maximum depth. Thereafter, the siphon drain of the present invention becomes operative to drain the water from the roof down to a predetermined minimum level. The operation of the drain valve of the present invention is completely automatic, and does not require operator intervention to render it operative. Moreover, the drain valve of the invention is structured such that there is no danger of the stored product being accidentally leaked or drained from the tank through the water drain valve.